Stainless steel and method



United States Patent Q STAINLESS STEEL AND METHOD Harry Tanczyn, 4014 Fairfax Road, Baltimore, Md.

N Drawing. Filed Dec. 18, 1957, Ser. No. 703,505

13 Claims. (Cl. 75-125) My invention is generally concerned with austenitic chromium-nickel stainless steels and more particularly relates to a heat-hardenable austenitic stainless steel, the method of hardening the same and the hardened steel, itself, as well as various articles fashioned thereof.

Among the objects of my invention is the provision of a stainless steel which is substantially fully austenitic; which is readily hot-workable as by rolling, drawing, piercing, extruding and the like, in the fabrication of castings, plate, sheet or strip, bars, rods, wire, tubes and special shapes; which steel is hardenable by heat-treating methods employing heat-treating temperatures which are so low as to minimize scaling, thereby avoiding objectionable ro'ughening of the surface by oxidation; and which heat-hardened steel is possessed of many beneficial physical properties such as good strength and corrosion resistance in the heat-hardened condition, all in combination with good hot-workability prior to heat-hardening.

Other objects of my invention in part will be obvious and in part pointed out hereinafter in the description which follows.

My invention, therefore, lies in the combination of elements, composition of ingredients, in the various operational steps and the relation of each of the same to one or more of the others, and in combination of composition and operational steps, the scope of the useful application of all of which is set forth in the claims at the end of this specification.

In order to gain a better understanding of certain features of my invention, it is to be noted at this point that the austenitic chromium-nickel stainless steels ordinarily are not considered to be hardenable by heat-treatment. I refer to the chromium-nickel stainless steels containing about 16% to 35% chromium, about 5% to 30% nickel, and the remainder principally iron. Of course, these steels contain carbon, manganese, silicon, phosphorus and sulphur in small amounts. And they also may include one or more of molybdenum, tungsten, columbium and titanium for special purposes.

The various austenitic chromium-nickel stainless steels noted usually are hardened, where hardening is desired, by any one of a number of cold-working operations, such as cold-rolling, cold-drawing, cold-upsetting, and the like. As is well known, however, the austenitic chromiumnickel stainless steels which are hardened by cold-working have non-uniform mechanical properties, that is, the properties taken across the direction of working differ substantially from those taken along the direction of working. In many applications this non-uniformity in mechanical properties is found objectionable.

In recent years there have been developed a number of chromium-nickel stainless steels which by virtue of the addition of one or more special alloying ingredients have been made hardenable by heat-treating methods. For example, a chromium-nickel stainless steel containing substantial amounts of one or more of the strong carbideforming elements columbium and titanium are hardenable by an age-hardening treatment. The columbium addition, however, is quitecostly as well as being considered a strategic element. And titanium, although readily available, is inclined to give dirty metal, with resultant unpredictable loss in mechanical properties.

Even more recently there have been developed agehardening chromium-nickel stainless steels in which the desired age-hardening is had through the additio'n of aluminum, copper or beryllium. The aluminum addition, however, when made in substantial amounts, is inclined to cause scum formation during teeming. And the beryllium addition is found to be very expensive.

One of the objects of my invention is the provision of an austenitic chromium-nickel stainless steel employing available alloying elements, which steel possesses good hot-working properties, which readily'lends itself to hardening and strengthening by heat-treatment at temperatures which are not such as to cause objectionable scale-formation and heat-tinting, and which in the hardened condition is strong, tough and corrosion-resistant.

Referring now more particularly to the practice of my invention, I provide an austenitic chromium-nickel stainless steel of particular chromium and nickel contents in which there is included the two ingredients molybdenum and silicon, both in critical amount. The amounts of chro'mium and nickel also are critical; so, too, is the carbon content, all as more fully noted below.

In its broadest aspect the austenitic chromium-nickel stainless steel of my invention essentially consist of about 12% to 18% chromium, 13% to 30% nickel, 1% to 4.50% molybdenum, 3.0% to 6.5% silicon, with the sum of the molybdenum and silicon contents of at least about 5.5%, a carbon content not exceeding about 0.15%, and the remainder substantially all iron. Manganese, of course, is present, this in amounts up to 4%. And phosphorus and sulphur are present, each in amounts not exceeding 0.05 Where desired, there may be employed the additional ingredients copper. and/or tungsten. in

amounts up to 3%. So, also, columbium may be included in the steel in amounts up to 1%. And' nitrogen advantageously may be present in amounts up to 0.20%.

Preferably the steel analyzes about 13% to 16% chr'omium, 15% to 20% nickel, 2% to 4% molybdenum, 4.5% to 5.5% silicon, with a carbon content not exceeding .15%, and the remainder substantially all iron. A preferred steel analyzes about 14% chromium, 16% nickel, 3% molybdenum, 5% silicon, 0.05% carbon, 0.50% manganese, and remainder iron.

My steel in the form of castings and plate, sheet, strip, bars, rods, wire, tube and various special shapes, is hardened by an initial solution-treatment. at a temperature of about 2000" to 2300 F., followed by cooling to room temperature and re-heating at a temperature of about 1200 to 1500 F., the time at solution-treating temperature being on the order of one-half hour while that at the heat-hardening temperature being about 24 hours. Preferably I harden the steel by initial solutiontreating temperature at about 2000 to 2200 F. and cooling, followed by re-heating at a temperature of 1100 to 1600 F. I find that with the lower maximum solution-treating temperature there is less likelihood of burning the steel. The preferred heat-hardening temperature is about 1300" to 1400 F. because Within this range I find that maximum final hardening is achieved, there being where the carbon content exceeds the 0.15% figure, the

loss there being attributed to excessive hardness in the solution-treated condition.

The critical character of the carbon content of my steel is revealed in the test results reported in Table 1 below, in which for a chromium-nickel-molybdenum-silicon stainless steel there is indicated the efiect on hotworkability and initial hardness, that is, hardness in the annealed condition, for three steels of differing carbon contents.

It will be seen that as the carbon increases above about 0.15%, the hardness in the annealed condition, that is, heating at 2200 F. for one-half hour and then waterquenching, immediately suffers and there results a corresponding loss in hot-workability. The sample with the carbon content of 0.148% has a hardness in the annealed condition of Rockwell B 93 and good hot-workability. For the samples with carbon contents of 0.264% and 0.402%, the annealed hardness respectively amounts to Rockwell B 97 and C 22, with only fair hot-workability for both.

The hot-workability of the austenitic chromium-nickelmolybdenum-silicon steel also suffers where the chromium content exceeds about 18%, as illustrated by the tests reported in Table II below:

TABLE II Efiect of chromium content on hot-workability Hot;- Heat No. 81 Cr N1 M0 Work ability 061 5. 02 16. 12 20.12 3.90 Fair. 062 5. 13 17. 92 20. 16 3. 85 Poor 053 5. 07 19. 91 20.03 3. 87 Poor nickel free ferrite appears. At least 15% nickel is required in order to maintain a fully austenitic structure and desired hot-working characteristics. The latter is illustrated for a series of chromium-nickel-molybdenum-silicon stainless steels, these of differing molybdenum contents and nickel contents of 15%, 20% and 25%, being given in Table III below:

TABLE III Efiect of nickel content on hot-workability Hot- Rockwell Heat No. O 81 Or N1 M0 Work- Hardness, ability 2,200 F.,

% hr. WQ,

4. 78 14. 47 27. 3. 73 Good B 91 5. 25 13. 95 25. 01 3. 02 Good 13 91 5. 35 13.97 20. 17 1.06 Good B 84 5. 42 14. 15 20. 21 2. 10 Good B 86 5. 37 13. 95 20. O8 3. 98 Fair B 88 5. 44 14. 25 15. 14 1. 07 Good B 89 5. 37 14. 08 15. 21 2. 07 Good B 90 5. 41 14.16 15. 22 3.93 Fair B 99 It will be seen from the figures given in Table III above that good hot-workability is had with the steels of 15%, 20% and 25% nickel in every case except where both the molybdenum and silicon contents are high, in

which event there is a loss in hot-workability.

The silicon and molybdenum contents of my steel both are highly critical. Where the silicon content is less than about 3.0% there is some loss in the desired resistance to scaling, and where it exceeds 6.5% there is a sharp loss in hot-workability. The loss of hot-workability even without the complicating effect of molybdenum, is illustrated in the results presented in Table IV below for an austenitic chromium-nickel stainless steel of difiering sili- It will be seen that with the samples with silicon contents of 4.58% and 5.25%, the hot-workability is good, while the samples with silicon content of 7.02% and 8.32% the hot-workability is poor.

The effect of silicon in combination with molybdenum on the hot-workability of the chromium-nickel-molybdenum-silicon stainless steel is seen from the results given in Table V below, in which for silicon contents of about 3%, 4% and 5%., there are molybdenum variations from 1% to 5%.

TABLE V Efiect of silicon and molybdenum contents on hot-workability Rockwell Hardness Hot- Hest No. 0 81 01 N1 M0 Work- 2,200 F., 2,200 F., 34 hr. ability 1411:. WQ WQ 1,300

24 hr. WQ

3.20 14.01 28.13 1.00 Good B 72 B 93 3.15 14.20 28 20 2.02 Good B 73 B 96 3.25 14.17 27.98 3.84 Good B 75 c 22 3.97 13.91 27.88 1.05 Good B B 97 3.90 13.98 27.95 2.02 Good B 79 o 22 3.95 14.01 27.78 3. 84 Good B 83 0 27 5.05 13.82 28.21 1.91 Good B 91 o 28 4.73 13.99 28.10 3.35 Good B 91 o 33 5.29 13.64 28.20 4. 88 Fair B 93 o 36 The data reported in Table V above reveals the loss in hot-workability which is sutfered where, in the chromi um-nickel-molybdenum-silicon austenitic stainless steel, there is employed a molybdenum content exceeding 4.5% The data also clearly shows, however, that where the articles and products of ultimate use. Illustratively, it is suited to use in the form of plates, sheet, tubing and the like, in pressurized water reactors, heat-exchangers, and interconnecting piping.

5 Thus it will be seen that I have provided in my invensum of the molybdenum and silicon contents is less than tion a heat-hardenable austenitic chromium-nickel-moabout 5.5%, final hardness, that is, hardness after solulybdenum-silicon stainless steel which is possessed of tion-treating and heat-hardening, is wholly inadequate. many highly desirable characteristics. The steel of my The ranges of molybenum and silicon in my steel, thereinvention possesses good hot-workability in combination fore, are both highly critical. with satisfactory hardness and strength in the heat-hard- As specifically illustrative of the chromium-nickelened condition. It is strong, durable and corrosion-remolybdenum-silicon austenitic stainless steels of my insistant. It possesses excellent stress-corrosion characvention I give two examples in Tables VI(a) and VI(b) teristics. below, the chemical analyses of these two steels being A many possible embodiments may be made of my given in Table h mechanical Properties in invention and as many changes may be made in the emthe fully hardened condition 1n Table VI(b): bodiments hereinbefore set forth, it will be understood TABLE VI(a) that all matter described herein is to be interpreted as illustrative and not by way of limitation. Chemical analyses of two chromium-makel-molybdenum- I claim as my invention:

slhcon austemtlc stamless steels l. A fully austenitic heat-hardenable stainless steel of good hot-working characteristics and consisting essen- Heat C 51 of N I tially of about 12% to 18% chromium, 15% to 30% nickel, 3.00% to 6.50% silicon, 1% to 4.50% molyb- %:i23i:::::::::::1331;331:313 23%? 2313 1233i 531%? 3:33 denum, with the sum of the molybdenum Silicon 25 contents at least about 5.5%, carbon not exceeding 0.15 max P and max copper up to 3%, tungsten up to 3%, columbium up to TABLE VI(b) Mechanical properties of the steels of table VI(a) Rock. Ult.Tens..02%Yld. 2% Yld. Red. of Elong., Heat No. Condition Hard. Stu, Str., Str., Area, 2"

p.s.i. p.s.i. p.s.i. percent percent 2,150 F.1 hr 0 33 154,000 65,000 83,600 32.0 9.5 E4549 i 155, 000 500 as, 000 35. 0 11. 0 130,000 48,000 05, 200 38.8 18.5 E4695 129,000 48, 700 05, 700 40.0 22.0

One of the specific examples of my stainless steel (the Heat E.4549--2 samples being tested) in the solutiontreated and heat-hardened condition, has a Rockwell Hardness of C 33, an average ultimate tensile strength of 154,500 p.s.i. and a .2% yield strength averaging 84,300 p.s.i. The other specific examples (Heat E.46952 samples being tested) in the final heat-hardened condition has a Rockwell Hardness of C 28, an ultimate tensile strength averaging 129,500 p.s.i. and an average .2% yield strength of 65,400 p.s.i.

The steel of my invention is resistant to heat-scaling, resistant to intergranular oxidation and to carburization. Moreover, it is resistant to corrosion under stress. Thus four examples of Ms" strip analyzing about 14.24% chromium, 18.02% nickel, 2.91% molybdenum, 5.06% silicon, .027% carbon, 0.65% manganese, 0.008% phosphorus, 0.012% sulphur, and remainder iron, in different conditions of heat-treatment Were pickled and bent into U-shape with an applied stress of 80,000 p.s.i. and exposed for 492 hours in boiling molten hydrated magnesium chloride salt without developing any stress-corrosion cracking. The heat-treatment ranged from a simple solution-treatment at 2100 F. for 20 minutes and Waterquenched for one example to the solution-treatment plus heat-hardening treatment at 2100 F. and/or 1400 F. at 24 hours, respectively, for the other three. As compared to my steel, controlled samples of annealed type 304 chromium-nickel stainless steel strip, this analyzing about 18.78% chromium, 9.89% nickel, 0.065% carbon, 0.54% manganese, 0.018% phosphorus, 0.011% sulphur and remainder iron, when bent and stressed to 40,000 p.s.i., developed cracks in less than 24 hours in the boiling magnesium chloride salt.

The steel of my invention is suited to the production of a wide variety of corrosion-resisting and heat-resisting 1%, nitrogen up to- 0.20%, and remainder substantially all iron.

2. A fully austenitic heat-hardenable stainless steel of good hot-working characteristics and consisting essentially of about 12% to 18% chromium, 15% to 30% nickel, 3.00% to 6.50% silicon, 2% to 4.50% molybdenum, with the sum of the molybdenum and silicon contents at least about 5.5%, manganese up to 4%, car bon not exceeding 0.15% and remainder substantially all iron.

3. An austenitic heat-hardenable stainless steel consisting essentially of about 13% to 16% chromium, 15 to 20% nickel, 2% to 4% molybdenum, 4.5 to 5.5% silicon, carbon not exceeding 0.15%, and remainder substantially all iron.

4. An austenitic heat-hardenable stainless steel consisting essentially of about 14% chromium, 16% nickel, 3% molybdenum, 5% silicon, carbon not exceeding 0.15 and remainder substantially all iron.

5. In the production of a heat-hardened austenitic chromium-nickel stainless steel, the art which includes providing a steel consisting essentially of about 12% to 18% chromium, 13% to 30% nickel, 3.00% to 6.50% silicon, 1% to 4.50% molybdenum, with the sum of the molybdenum and silicon contents at least 5.5 manganese up to 4%, carbon not exceeding 0.15%, and remainder substantially all iron; heating the steel at a temperature of 2000 to 2300 F. and cooling; and thereafter reheating the same at a temperature of 1200 to 1500 F.

6. In the production of a heat-hardened austenitic chromium-nickel stainless steel, the art which includes pro viding a steel consisting essentially of about 12% to 18% chromium, 15% to 30% nickel, 3.00% to 6.50% silicon, 1% to 4.50% molybdenum, with the sum of the molybdenum and silicon contents at least about 5.5 man- 7 ganese up to 4%, carbon not exceeding 0.15%, and remainder substantially all iron; heating the steel at a temperature of 2000 to 2200 F. and cooling the same to achieve phase transformation; and thereafter reheating the transformed steel at a temperature of 1100 to 1600 F to achieve heat-hardening.

7. In the production of a heat-hardened austenitic stainless steel the art which comprises providing a steel consisting essentially of about 13% to 16% chromium, 15% to 20% nickel, 2% to 4% molybdenum, 4.5% to 5.5% silicon, carbon not exceeding 0.15 and remainder substantially all iron; heating the steel at a temperature of 2000 to 2200 F. and cooling; and reheating at a temperature of about 1300 to 1400 F.

8. A heat-hardened austenitic chromium-nickel stainless steel consisting essentially of about 12% to 18% chromium, 13% to 30% nickel, 3.00% to 6.50% silicon, 1% to 4.50% molybdenum, with the sum of the molybdenum and silicon contents at least about 5.5%, manganese up to 4%, carbon not exceeding 0.15%, copper up to 3%, tungsten up to 3%, columbium up to 1%, nitrogen up to 0.20%, and remainder substantially all iron.

9. A heat-hardened austenitic chromium-nickel stainless steel consisting essentially of about 13% to 16% chromium, 15% to 20% nickel, 2%v to 4% molybdenum, 4.5% to 5.5% silicon, carbon not exceeding 0.15%, and remainder substantially all iron.

10. A heat-hardened austenitic chromium-nickel stainless steel consisting essentially of about 14% chromium, about 16% nickel, about 3% molybdenum, about 5% silicon, carbon not exceeding 0.15 and remainder substantially all iron.

11. A heat-hardened austenitic chromium-nickel stainless steel consisting essentially of about 15 chromium, 15% nickel, 3% molybdenum, 5% silicon, carbon not exceeding 0.15%, and remainder substantially all iron.

12. A heat-hardened austenitic chromium-nickel stainless steel consisting essentially of about 15 chromium, 21% nickel, 4% molybdenum, 4% silicon, carbon not exceeding 0.15%, and remainder substantially all iron.

13. A heat-hardened austenitic chromium-nickel stainless steel consisting essentially of about 14% chromium, 18% nickel, 3% molybdenum, 5% silicon, carbon not exceeding 0.15%, and remainder substantially all. iron.

References Cited in the file of this patent UNITED STATES PATENTS 2,401,580 Mohling June 4, 1946 2,553,330 Post et al. May 15, 1951 2,839,392 Streicher June 17, 1958 2,861,883 Mott Nov. 25, 1958 FOREIGN PATENTS 53,768 Holland Jan. 15, 1943 1,083,154 France June 23, 1954 511,160 Canada Mar. 22, 1955 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,984,563 May 16, 1am

Harry Tanczyn It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, lines 1, 2, and 3, for "Harry Tanczyn, of

Baltimore, Maryland," read Harry Tanczyn, of Baltimore, Maryland, assignor to Armco Steel Corporation, a corporation of Ohio, line 12, for "Harry Tanczyn, his heirs" read Armco Steel Corporation, its successors in the heading to the printed specification, line 3, for "Harry Tanczyn, 4014 Fairfax Road, Baltimore, Md." read Harry Tanczyn,

Baltimore, Md. assignor to Armco Steel Corporation, a corporation of Ohio Signed and sealed this 17th day of October 1961,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A FULLY AUSTENITIC HEAT-HARDENABLE STAINLESS STEEL OF GOOD HOT-WORKING CHARACTERISTICS AND CONSISTING ESSENTIALLY OF ABOUT 12% TO 18% CHROMIUM, 15% TO 30% NICKEL, 3.00% TO 6.50% SILICON, 1% TO 4.50% MOLYBDENUM, WITH THE SUM OF THE MOLYBDENUM AND SILICON CONTENTS AT LEAST ABOUT 5.5%, CARBON NOT EXCEEDING 0.15%, COPPER UP TO 3%, TUNGSTEN UP TO 3%, COLUMBIUM UP TO 1%, NITROGEN UP TO 0.20%, AND REMAINDER SUBSTANTIALLY ALL IRON. 